1. Field of the Invention
The invention relates to an electric vehicle having a motor to propel the electric vehicle, a secondary battery that exchanges power with the motor via a power line, and a capacitor connected to the power line. The invention also relates to a control apparatus and a control method for the electric vehicle.
2. Description of Related Art
A vehicle including an alternating current motor to propel the vehicle, an inverter that converts direct current power into alternating current power and supplies the alternating current power to the motor, a storage device such as a secondary battery, a converter that boosts a voltage of the storage device and supplies the boosted voltage to the inverter, a relay capable of connecting and disconnecting the storage device to and from a power supply line that connects the converter and the inverter, and a smoothing capacitor connected to the power supply line on a high voltage side of the converter has been proposed in the related art as this type of electric vehicle (see WO2010/131353A1, for example). When a collision is detected in this vehicle, power generated by a residual charge of the capacitor is consumed by controlling the converter such that a voltage boosting operation and a voltage reducing operation are performed repeatedly, thereby increasing switching loss, or controlling the inverter such that only a field current component (a d axis current) is supplied to the motor, thereby increasing motor loss. At this time, discharge of the residual charge of the capacitor is promoted by reducing respective gate voltages of the inverter and the converter below normal levels in order to increase the switching loss of switching elements provided in the inverter and the converter.
A rotary shaft of the motor is normally coupled to a drive wheel via a gear mechanism, but when the vehicle is involved in a collision, a resulting impact may disconnect the coupling of the rotary shaft. As a result, the motor continues to rotate. In this case, a comparatively large counter-electromotive voltage is generated in the motor and charges accumulate in the capacitor. Accordingly, it may take a long time to discharge the residual charge of the capacitor completely.